This invention relates generally to cleanliness measurement and more particularly to a quantitative measurement of surface particulate contamination of mechanical system components.
Surface particulate contamination is a well-known source of mechanical system failures. This is particularly the case in power generating systems such as gas turbines where particulates can cause abrasion at the interface of moving parts, contaminate fluids flowing through the system, erode structures in high velocity fluid flow paths, and create deposits that either reduce desired flows or insulate against desired heat transfer. The provision of filters can control the flow of particulate contaminants into the system during operation. However, system components can become contaminated with particles during manufacture and assembly thereof. The presence of contaminants on components during assembly, which will not be captured by the filters, can result in the mechanical failures noted above.
A number of approaches to verify surface cleanliness of mechanical system components has been proposed. One such approach is the well known xe2x80x9cwhite glove testxe2x80x9d in which an inspector wipes a gloved finger across the surface of the component for some distance, and then observes the resultant stain on the finger. The inspector is then required to make an arbitrary decision as to the amount of contamination removed based on the darkness of the stain. This approach is highly subjective and varies greatly from test-to-test and from inspector-to-inspector. A more objective approach involves measuring particulate concentrations in the fluids used to wash the components. The fluid concentrations are typically determined using light attenuation or refraction, often with laser beams. However, this approach does not lend itself to practical, economic use on a mechanical assembly floor.
Another approach employs the use of xe2x80x9csurface replicas.xe2x80x9d Here, the component surface to be sampled is covered with either an adhesive tape or a curable material that replicates the surface topography while also capturing loosely held surface particulate contamination. The surface is then scanned manually or with sophisticated optical recognition software to count particle numbers and sizes. This approach cannot give near instantaneous results on the factory floor and would be prohibitively expensive in most cases. Moreover, the sampled surface area is, by design, exactly equal to the size of the removed sample. Therefore, no amplification of the sampled area can be obtained.
Accordingly, there is a need for a quick, quantitative measurement of surface cleanliness for the factory floor assembly of mechanical system components.
The above-mentioned need is met by the present invention which provides an apparatus for measuring surface particulate contamination that includes a tool for collecting a contamination sample from a target surface, a mask having an opening of known area formed therein for defining the target surface, and a flexible connector connecting the tool to the mask. The tool includes a body portion having a large diameter section defining a surface and a small diameter section extending from the large diameter section. A particulate collector is removably, mounted on the surface of the large diameter section for collecting the contaminants. The tool further includes a spindle extending from the small diameter section and a spool slidingly mounted on the spindle. A spring is disposed between the small diameter section and the spool for biasing the spool away from the small diameter section. An indicator is provided on the spindle so as to be revealed when the spool is pressed downward to compress the spring.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.